The Eucharist, as a sacrament, produces in you an increase of habitual, or sanctifying, grace by its own power. Its effects are like those of food: it maintains, increases, and repairs your spiritual forces, causing also a joy that is not necessarily felt, yet it is real.
Holy Communion not only preserves the life of your soul, but increases it, just as the body is not only supported by means of natural food, but increases in strength.
Holy Communion also preserves and increases all the various virtues, which are bestowed upon your soul together with sanctifying grace. By increasing the theological virtues (faith, hope, and charity), Holy Communion enables you to enter into closer union with God, and by strengthening the moral virtues (prudence, temperance, justice, and fortitude), Holy Communion enables you to regulate better your whole attitude toward God, your neighbor, and yourself. By rendering the seven gifts and the twelve fruits of the Holy Spirit more abundant, Holy Communion opens your understanding and will to the inspirations and promptings of the same Holy Spirit.
The Holy Spirit sanctifies souls by the supernatural gift of grace. The highest type of grace is sanctifying grace, which is a spiritual quality, dwelling in our soul, making it like God Himself. Our Lord spoke of the reception of this life as a spiritual birth when He said to Nicodemus, “Unless one is born anew, he cannot enter the kingdom of God.”
Sanctifying grace is also called habitual grace, because once we have received it, it remains as a habit in our soul. Once it has been received, sanctifying grace remains in the soul unless it is driven out by mortal sin.